I have used a Astro-Physics 900GTO mid-sized GEM with various OTAs since 2001. I like its build quality, tracking accuracy, and smooth operation but can be a bit noisy moving at its faster slew rates. Does anyone know of or use a GEM, for OTAs of 25-45 lbs., with quieter motor assemblies? Is the A-P Mach 1 GEM also as noisy? IIRC, I had a Tak NJP GEM back in 2000 that was quieter.

hmm i doubt it. My mach1 which has the same motor and gearbox as the 900, even at the lower slew speeds it's pretty loud. I have actually not heard an ASA in person but judging by the videos that I have seen they essentially produce no easily audible noise because they have no gears.

I don't use the two highest slew speeds on my 900GTO. If I need to move the scope to a new object more than a few degrees, I manually reposition the OTA. Besides, high-speed slewing really uses up your battery power - a lot more than tracking. If you want to get longer life ut f your battery, say at a remote star party, then don't power slew all night. Use your hands and manually move reposition the scope to the new area of the sky. I only use the lower slew speeds - the ones you use centering an object in a optical finder or lowest power eyepiece view. That's the beauty of a tracking GEM. I don't use GoTo on the 900 mount either. So, high speed slewing object-to-object producing loud motor assembly noise is avoided. It is irritating to my hearing and I'm sure neighboring observers don't like it either. Two things I don't like being in a field with many other observers at a star party: 1. Bright laptops and LED devices; 2. Nearby loud GoTo slewing for hours on end.

I have the AP900. I think if you cut down the max slew speed it would be much quieter.

I think the next best thing A-P could do for their mounts is to develop lower-noise drive assemblies. What makes this noise anyway? Is it the fine Swiss motors or the gears? With direct drive assemblies, aren't there still gears used (reduction gears)?

hmm i doubt it. My mach1 which has the same motor and gearbox as the 900, even at the lower slew speeds it's pretty loud. I have actually not heard an ASA in person but judging by the videos that I have seen they essentially produce no easily audible noise because they have no gears.

The EQ6/Atlas is a very quiet mount. That ASA is amazingly silent! My Mach 1 used to be very noisy, especially the dec gears. I reset the gear mesh on both axis and there certainly was an improvement...it used to sound like a coffee grinder It's a simple two minute procedure and there are no actual adjustments to make. It's just a matter of loosening and retightening the bolts. Have you guys tried this on the Mach's?

I did this on my Mach1. No difference on noise. But prior to the adjustment my CP3 controller got very very hot - kettle of boiling water hot - (I think the gears were meshed too tightly, which overloaded the motors).

The noise is the only complaint I have with the Mach1. The ASA is certainly quiet. Given a chance to redo my mount situation I would still go with the Mach1, the ASA mounts are not the all around performer I require, at least going on what I last knew of them.

There are still times I long for a more gentle sound on the AP though.